JPH074833A - Separation of air - Google Patents

Abstract

PURPOSE: To separate impure oxygen product from air while operating a high pressure rectification column under an especially low pressure at the bottom part thereof because of a specified pressure at the bottom part of a low pressure rectification column. CONSTITUTION: First stream of compressed, cooled air is introduced into a high pressure rectification column 12 through an inlet 14 and is separated into nitrogen vapor and oxygen enriched liquid. At least some of the nitrogen vapor is condensed in a condenser 22 and one stream of resulting liquid nitrogen is used as reflux in the column 12 and another stream as reflux in a low pressure rectification column 30. Oxygen enriched liquid withdrawn from the column 12 through an outlet 32 is separated in the column 30. Impure liquid oxygen product is withdrawn from the column 30 through an outlet 52. A less pure stream of liquid oxygen is withdrawn from the column 30 through an outlet 48, is reboiled in condenser-reboiler 16 by indirect heat exchange with a second stream of air and is reintroduced into from the column 30 at its bottom through an inlet 51.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to a method and apparatus for separating air.

[0002]

The most important method for commercial air separation is by rectification. The most frequently used air separation cycle is to produce a compressed air stream by compressing the air stream, purifying the compressed air stream produced by removing water vapor and carbon dioxide, and cooling it by heat exchange with the compressed air stream. It includes the steps of returning the stream to a temperature suitable for its purification. The rectification includes so-called "double rectification tower" including high-pressure rectification tower and low-pressure rectification tower.
(double rectification column), ie one of the two columns is operated at a higher pressure than the other. The air is mostly, but not all, of the high pressure rectification column. And is separated into oxygen-enriched liquid air and liquid nitrogen vapor, the nitrogen vapor is condensed, and part of the condensate is used as the liquid reflux agent in the high pressure rectification column. The liquid is withdrawn from the bottom of the higher pressure rectification column, subcooled and introduced into the intermediate region of the lower pressure rectification column via a throttle valve or pressure reducing valve. , Separated into substantially pure oxygen and nitrogen products, which are withdrawn in vapor form from the lower pressure rectification column, with which the incoming air forms a return stream with which it exchanges heat. Liquid reflux agent for low pressure rectification column collects the rest of condensate from high pressure rectification column It was subcooled, through a throttle valve or pressure reducing valve, by passing it through a top of the lower pressure rectification column, it is supplied.

Conventionally, a low pressure rectification column has an absolute atmospheric pressure of 1-1.
It is operated at a pressure within the range of 5. Liquid oxygen at the bottom of the lower pressure rectification column is used to match the condensation capacity at the top of the higher pressure rectification column. Thus, nitrogen vapor from the top of the higher pressure rectification column is heat exchanged with liquid oxygen at the bottom of the lower pressure rectification column. Thereby a sufficient amount of liquid oxygen is vaporized to meet the requirements for reboiling of the lower pressure rectification column and good production of the gaseous oxygen product is achieved. The pressure at the top of the higher pressure rectification column, and therefore the pressure at which the incoming air is compressed, is set so that the temperature of the condensed nitrogen is one or two Kelvin higher than the temperature of the boiling oxygen in the lower pressure rectification column. . As a result of these relationships, it is generally possible to operate high pressure rectification columns below a pressure of about 5.5 bar.

Oxygen products are not of high purity, for example
Improvements have been proposed to air separation processes in which the high pressure rectification column is operated at pressures below 5.5 bar when it contains 3 to 20% by volume of impurities. US-A-4 410 343 (Zimer)
When such low-purity oxygen is needed,
Rather than having the above-mentioned links of the low pressure rectification column and the high pressure rectification column ring, the air provides reboil to the low pressure rectification column and oxygen at the bottom of the low pressure rectification column to evaporate the oxygen product. Used to bring to a boil. Next, the generated condensed air is supplied to both the high pressure rectification column and the low pressure rectification column. The oxygen-enriched liquid stream is withdrawn from the high pressure rectification column,
It passes through a throttle valve, a part of which is used for the condensation of nitrogen at the top of the higher pressure rectification column.

US-A-3 210 951 also provides reboiling to the low pressure rectification column to evaporate the oxygen product, so that air is used to boil oxygen at the bottom of the low pressure rectification column. Disclosed is a method for producing impure oxygen. However, in this example, oxygen-enriched air from the middle region of the lower pressure rectification column is used to serve to condense the nitrogen vapor produced in the higher pressure rectification column. This method can, at least theoretically, reduce the operating pressure of the high pressure rectification column to below 5 bar.

[0006]

SUMMARY OF THE INVENTION The present invention provides an impure oxygen product from air which, due to the predetermined pressure at the bottom of the low pressure rectification column, allows the high pressure rectification column to operate at a particularly low pressure at its bottom. And a method for separating the same. For example, if the pressure at the bottom of the low pressure rectification column is 1.4
If on the order of bar, the process according to the invention can be operated at a pressure of the order of 3 bar at the bottom of the higher pressure rectification column.

[0007]

According to the invention, a first air stream is rectified in a high pressure rectification column, whereby nitrogen vapor and oxygen-enriched liquid are produced; Condensing at least some of the condensate, using a first stream of the condensate produced as a reflux agent in the higher pressure rectification column, and a second stream of the condensate as a reflux agent in the lower pressure rectification column. Removing the oxygen-enriched liquid stream from the high pressure rectification column and rectifying it in the low pressure rectification column, whereby
Producing impure liquid oxygen product; removing the impure liquid oxygen product from the low pressure rectification column in a liquid state;
An intermediate stream of liquid whose oxygen concentration is higher than that of the oxygen-enriched liquid but lower than that of the impure liquid oxygen product is taken out of the low-pressure rectification column, and the intermediate stream is fed to the second air. Reboiling by heat exchange with the stream and returning the resulting reboiled intermediate stream to the bottom region of the low pressure rectification column to provide an upward reboiling liquid stream through the low pressure rectification column. A method of separating air including is provided.

The invention also provides a high pressure rectification column for separating a first stream of air into a nitrogen vapor and an oxygen enriched liquid, an inlet for the oxygen enriched liquid withdrawn from said high pressure rectification column. A low-pressure rectification column for producing an impure liquid oxygen product having, a condenser for condensing nitrogen separated in the high-pressure rectification column, the high-pressure rectification column using the resulting condensate as a refluxing agent, and Means for feeding into the low pressure rectification column, an outlet from the low pressure rectification column for the impure liquid oxygen product, from the low pressure rectification column in a region intermediate the inlet and the outlet A reboiler for boiling the intermediate stream of liquid withdrawn by heat exchange with a second stream of air, and air comprising means for returning the reboiled liquid produced to the bottom of said lower pressure rectification column. A device for separating is provided.

The intermediate stream necessarily has a lower temperature than the impure liquid oxygen product, so that when heat exchange takes place between the second air stream and the impure liquid oxygen product, Allows heat exchange between the second air stream and the resulting intermediate stream in the lower temperature range. If the second air stream condenses at least in part, preferably sufficiently, by heat exchange with its intermediate stream, it is therefore impure liquid oxygen for feeding the reboiler to the lower pressure rectification column. A second air stream pressure is used that is lower than the pressure required to boil the product. Since the second air stream condenses and the middle stream reboils within the discrete temperature range, it is possible to match the temperature-enthalpy distribution of the second air stream with that of the reboil middle stream, thus Effective heat exchange between the two streams is possible. The oxygen content of the intermediate stream is preferably 50-85% by volume, most preferably 75% by volume.
Is the order.

The nitrogen vapor produced in the high pressure rectification column is preferably condensed by heat exchange with oxygen-enriched air. The oxygen-enriched liquid stream is preferably used for this purpose, whereby it is at least partly reboiled. Thus,
At least a portion of the oxygen-enriched liquid stream is vaporized upstream of its introduction into the lower pressure rectification column.

The first and second air streams are preferably
Carbon dioxide and water vapor are respectively removed from the compressed air stream and the resulting purified air stream is subjected to countercurrent heat exchange with the impure liquid oxygen product and the nitrogen stream withdrawn from the low pressure rectification column. Formed by cooling in the main heat exchanger, the nitrogen stream is withdrawn from the lower pressure rectification column.

The low pressure rectification column has a pressure of 1.5 at the bottom.
When operating on the order of bar or lower, the impure liquid oxygen product is preferably removed from the lower pressure rectification column by a pump which raises the product pressure to the required feed pressure and impure. Pure liquid oxygen is vaporized by its passage through the main heat exchanger. In order to achieve sufficient heat exchange, the vaporization of the impure liquid oxygen product is preferably carried out with the third air stream at a pressure higher than the pressure of the first air stream or the pressure of the second air stream. Heat is exchanged in the heat exchanger. This third air stream is preferably at least partially condensed thereby, but this pressure is not supercritical. Part or at least part of the fully condensed third air stream is preferably introduced into the higher pressure rectification column. The second air stream is also preferably introduced into the higher pressure rectification column downstream of heat exchange with its intermediate stream.

If the bottom of the lower pressure rectification column is operated at a pressure substantially higher than 1.5 bar, the impure liquid oxygen product is preferably reduced in pressure and directed towards nitrogen vapor. It is vaporized from the high-pressure rectification column by flow heat exchange.

The cooling requirements for the method according to the invention are:
Filled by using at least one expansion turbine and performing external work and expansion in a high pressure stream of air or nitrogen. Preferably, a portion of the third air stream is then taken and expanded to the pressure in the high pressure rectification column with the performance of external work in the turbine, at least a portion of the expanded air being high pressure rectification. Introduced to the tower. If desired, the expanded portion of the third air stream may be
It is combined with the second air stream upstream of heat exchange with the intermediate stream of the second air stream. Alternatively, the portion of the third air stream can be expanded in the turbine to the pressure of the low pressure rectification column and the expanded air produced can be introduced into the low pressure rectification column. Another alternative is to take a nitrogen stream from the high pressure rectification column, warm the stream and then expand it in a turbine to produce the cooling required for the method according to the invention. However, typically, depending on the operating pressure of the high pressure rectification column, the turbine is taken by taking a stream of nitrogen from the high pressure rectification column, warming it to ambient temperature, compressing it, and then cooling it. It is also necessary to create a stream of nitrogen for expansion within.

The method and the device according to the invention are very suitable for producing impure oxygen products containing up to 93% by volume of oxygen. At this time, the high pressure rectification column is operated at a low pressure of about 3 bar.

The method and device according to the present invention will now be illustrated with reference to the accompanying drawings.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Each of FIGS. 1 to 3 is a schematic process system diagram of an air separation plant.

Referring to FIG. 1 of the drawings, air is compressed in a compressor 2 to a pressure of 3 bar. The resulting compressed air stream passes through a purifier or unit 4, which is effective for removing water vapor and carbon dioxide from the air. Unit 4 performs this removal of water vapor and carbon dioxide,
Use a bed of adsorbent (not shown). The beds are typically operated out of series with one another such that one or more of the beds are used to purify air while the rest is regenerated, for example, by a hot nitrogen stream. The above purification devices and their operation are well known in the art and need not be described further.

The purified air stream passes through the main heat exchanger 6 from its warm end 8 to its cold end 10. Thereby the air stream is reduced in temperature from about ambient temperature to a temperature suitable for its separation by rectification. The air stream typically leaves the cold end 10 of the main heat exchanger 6 as steam at its separation temperature. The air stream is then split into first and second streams. The first air stream is introduced into the bottom region of the high pressure rectification column 12 via the inlet 14. The high-pressure rectification column 12 has a gas-liquid contact device (not shown), whereby the descending liquid phase uniformly contacts the ascending vapor phase, and mass transfer occurs between the two phases. The gas-liquid contact means is
For example, it includes a distillation tray (preferably sieve-like) or packing (preferably molded packing). In operation of the high pressure rectification column 12, liquid is collected at the bottom thereof. Since the first air stream is introduced at the bottom of the high pressure rectification column 12, the liquid at the bottom of the column 12 is in near equilibrium with such air and oxygen is the other major constituent of the air ( Since it is less volatile than nitrogen and argon), this liquid contains a higher molar fraction of oxygen than in the incoming gaseous air. Typically, the high pressure rectification column 12 is designed to hold a sufficient number of theoretical plates capable of producing substantially pure nitrogen vapor at the top thereof.

Thus, the high pressure rectification column 12 produces an oxygen-enriched liquid fraction at its bottom and a nitrogen vapor fraction at its top. The second air flow is the first condenser-reboiler 16
Through which it is fully condensed. The condensed second air flow is introduced into the inlet 1 located above the inlet 14.
It flows into the high-pressure rectification column 12 via 8.

The liquid nitrogen reflux agent for the high pressure rectification column 12 takes nitrogen vapor therefrom via an outlet 20 at the top thereof, condenses and introduces nitrogen vapor in a second condenser-reboiler 22. It is formed by returning the condensed nitrogen stream to the top of rectification column 12 via port 24. The other stream of condensed nitrogen is subcooled in the heat exchanger 26, passes through the pressure reducing valve or the throttle valve 28, and passes through the low pressure rectification column 3
It flows in as a refluxing agent at the top of 0. The low pressure rectification column 30 is
The same gas-liquid contactor (not shown) used in the high pressure rectification column 12 is provided so that the descending liquid phase is brought into uniform contact with the ascending gas phase and mass transfer occurs between the two phases. To do.

The stream of the oxygen-enriched liquid is taken out from the bottom of the high pressure rectification column 12 through the outlet 32, and the heat exchanger 3
Subcooled in 4 and flows through a pressure reducing or throttling valve 36. The oxygen-enriched liquid stream produced is split into two tributaries. The first tributary is the second condenser-reboiler 22.
Through which the cooling required for the condensation of the nitrogen vapor withdrawn from the higher pressure rectification column 12 via the outlet 20 is produced. The first oxygen-enriched liquid tributary boils as a result of heat exchange with condensed nitrogen vapor, and the resulting boiling oxygen-enriched liquid is introduced into the low pressure rectification column 30 via inlet 38. The second oxygen-enriched liquid tributary is introduced into the low pressure rectification column 30 via an inlet 40 located above the inlet 38. A liquid or vapor having a composition close to that of air is also withdrawn from the lower pressure rectification column 12 via outlet 42 and flows through a pressure reducing or throttling valve 44.
The depressurized fluid that is produced enters the low-pressure rectification column 30 via the inlet 46 located above the inlet 40. Inlet 38,
The fluid introduced into the lower pressure rectification column via 40 and 46 is then separated into nitrogen vapor and impure liquid oxygen. The pressure at the top of the rectification column 30 is typically
On the order of 1.3 bar.

To produce an upflow of vapor from the bottom to the top of the lower pressure rectification column 30, typically 75% by volume of oxygen is used.
Outlet 4 at a level at which the liquid containing
Liquid flow from the low pressure rectification column 30 via 8 (“intermediate”)
Flow) is taken out. The intermediate stream flows in heat exchange relationship with the second air stream countercurrently through the second air stream through the first condenser-reboiler 16. Thus, the cooling required to condense the second air stream is thus provided and the intermediate stream itself reboils. The generated boiling intermediate flow is reintroduced into the low pressure rectification column 30 via the inlet 51 in the bottom region of the low pressure rectification column 30.

As a result of the separation that takes place in the lower pressure rectification column 30, an impure liquid oxygen product, which typically contains on the order of 90% by volume oxygen, is formed at the bottom of the column 30. The impure liquid oxygen product stream is withdrawn from the bottom of the lower pressure rectification column 30 by pump 54 via outlet 52. Pumps typically pump impure liquid oxygen pressures to 8
Raise to bar or desired discharge pressure. The resulting pressurized impure liquid oxygen flows in the main heat exchanger 6 from its cold end 10 to its warm end 8, thereby
Evaporate and warm to near ambient temperature. Impure oxygen is used, for example, in combustion processes. The nitrogen flow is
It is taken out from the top of the low pressure rectification column 30 via the outlet 50. The nitrogen stream is sequentially heated by heat exchangers 26, 34 and 1
Flow through 0 and thus warm to near ambient temperature. Nitrogen is used in these heat exchangers 26, 34 and 10
Each of them flows from its cold end to its warm end. Nitrogen may be used in other processes or may be vented to the atmosphere.

In order to thermodynamically effect vaporization of the pressurized impure liquid oxygen product, a third air stream is generated at a higher pressure than the first and second streams, and this third stream is produced. Flow through the warm end 8 of the main heat exchanger 6 to its cold end 10. The third air stream takes a portion of the air stream from the middle of the refining unit 4 and the warm end 8 of the main heat exchanger 6 and compresses it in the compressor 56 to a pressure of 20.2 bar. Formed by. This pressure is sufficient to exchange heat and condense the third air stream with the boiling liquid oxygen product stream in the heat exchanger. The condensed third air stream is
Then, the pressure is reduced to a pressure substantially close to the operating pressure of the high pressure rectification column 12 by passing through the pressure reducing valve or the throttle valve.
Downstream of valve 58, the third air stream joins with the second air stream in the region intermediate the first condenser-reboiler 16 and the inlet 18 to the higher pressure rectification column 12.

The cooling requirement for the plant shown in the drawing is that a part of the third air stream is taken out of the main heat exchanger 6 at a temperature of about 151 K and the taken air is allowed to perform external work in the expansion turbine. It is caused by expanding.
If desired, the external work may be a compression mission.
The expanded air leaves the turbine 60 at a temperature of 92.4 K and at about the pressure of the higher pressure rectification column 12 a second air upstream of its path through its first condenser-reboiler 16. Join the flow.

Referring now to FIG. 2, there is shown an air separation plant essentially identical to that shown in FIG.
The same parts in FIGS. 1 and 2 are designated by the same reference numerals. The differences between the configurations / operations of the plant shown in FIG. 2 and the configurations / operations shown in FIG. 1 are as follows.

First, the outlet of the turbine 60 shown in FIG. 2 communicates with the inlet 62 of the low pressure rectification column 30, and communicates with the second air flow upstream of the condenser-reboiler 16. Not done (see Figure 1). Therefore, the expanded air leaving the turbine 60 flows directly into the low pressure rectification column 30.

Second, the outlet 4 from the high pressure rectification column 12
2, the pressure reducing valve 44, the inlet port 46 to the low pressure rectification column 30, and the associated pipe arrangement of the plant shown in FIG. 1 are all omitted from the plant shown in FIG. Thus, in the plant shown in Figure 2, the liquid or vapor stream is
It is not collected at all from the intermediate region of the high pressure rectification column 12 and is not introduced into the intermediate region of the low pressure rectification column 30.

Third, in the plant shown in FIG. 2, the main part of the condensed second air flow is the pressure reducing valve 5
Sampled from the upstream region of mixing of this stream with a third air stream in the downstream region of 8. A major portion of the condensed air stream flows through the expansion or decompression valve 64 and is introduced into low pressure rectification column 30 via inlet 66 at a level above that of inlet 62.

Fourth, in the plant shown in FIG. 2, all fluid through the pressure reducing valve 36 flows through the second condenser-reboiler 22, where it typically boils all. There is nothing to do. Thus, in the plant shown in FIG. 2, there is no inlet to the low pressure rectification column 30 corresponding to the inlet 40 shown in FIG.

In all other respects, the configuration and operation of the plant shown in FIG. 2 is substantially the same as that shown in FIG. 1, so that the plant and its operation shown in FIG. Further description is omitted.

However, examples showing the operation of the plant shown in FIG. 2 are shown in Tables 1 and 2 below.

[0034]

[Table 1]

[Table 2] In Figure 3 of the accompanying drawings there is shown a plant in which the low pressure rectification column is operated at a pressure of 4 bar and is capable of producing a pressurized nitrogen product without a nitrogen compressor for this purpose. There is. Referring to FIG. 3, the air is the main compressor 1
At 00 it is compressed to a pressure of 7.7 bar. The resulting stream of compressed air passes through a purifier or unit 102 that is effective in removing water vapor and carbon dioxide from the air. A bed of adsorbent is used in unit 102 to effect the removal of water vapor and carbon dioxide. Typically, the beds are operated out of sequence with each other, such that one or more of the beds are used to purify air while the rest is regenerated, for example, by a stream of hot nitrogen. . The above refining device and its operation are well known,
No further description is necessary.

The purified air is divided into first and second air streams. The first air stream sequentially flows through the first main heat exchanger 104 and the second main heat exchanger 106. The first air stream is thereby reduced to a temperature suitable for its separation by rectification. The first air flow is
It typically leaves the cold end of the second main heat exchanger as steam at its separation temperature. The first air flow is the inlet 110
Is introduced into the bottom region of the high pressure rectification column 108 via.
The high-pressure rectification column 108 has a gas-liquid contactor (not shown), whereby the descending liquid phase is brought into uniform contact with the ascending vapor phase, and mass transfer occurs between the two phases. The gas-liquid contacting means may be, for example, distillation trays (preferably sieve-like) or packings (preferably formed packings). In operation of the high pressure rectification column 108, liquid is collected at its bottom. Since the first air stream is introduced into the bottom region of the high pressure rectification column 108, the liquid at the bottom of the column 108 is in near equilibrium with such air and oxygen is the other major component of the air (nitrogen). And less than argon), the liquid contains a greater molar fraction of oxygen than the incoming gaseous air.
Typically, the high pressure rectification column 108 is designed with a sufficient number of theoretical plates so that substantially pure nitrogen can be produced at the top thereof.

The second stream of purified air is further compressed in booster-compressor 112 to a pressure of about 9.2 bar. In the booster-compressor 112, the second air stream is cooled to a temperature suitable for its separation by rectification, which cooling in turn is the main heat exchangers 104 and 106.
Is carried out by passing. The cooled second air stream enters via the first condenser-reboiler 114 from the cold end of the heat exchanger 106 where it is fully condensed. The condensed second air stream is split into two tributaries downstream of its passage through the first condenser-reboiler 114. One tributary flows through the throttle or pressure reducing valve 116 and is reduced in pressure to approximately the operating pressure of the higher pressure rectification column (about 7.5 bar). This tributary flows from the pressure reducing valve 116 into the high pressure rectification column 108 through the inlet 118. The other condensed air tributary flows via the pressure reducing valve 120, whereby the low pressure rectification column 1
The pressure is reduced to a pressure close to that of 22 (about 4.15 bar). The condensed air tributary flows from the pressure reducing valve 120 into the low pressure rectification column 122 via the inlet 124.

The liquid nitrogen reflux agent for the high pressure rectification column 108 is
Nitrogen vapor is then withdrawn at its top via outlet 126 and nitrogen vapor is removed to a second condenser-reboiler 128.
It is formed by condensing in and returning the condensed nitrogen produced through the inlet 130 to the top of the higher pressure rectification column. Another condensed stream of nitrogen is subcooled in the heat exchanger 132 and flows in via a throttle valve or pressure reducing valve 134. The generated liquid nitrogen flow is supplied from the pressure reducing valve 134 to the inlet port 136.
Through the column into the low pressure rectification column at its top and in column 122 acts as a reflux agent. Low pressure rectification column 12
2 is a gas-liquid contactor (not shown) similar to that used in the high pressure rectification column 108 for uniformly contacting the descending liquid phase with the ascending vapor phase and causing mass transfer between these two phases. No)). Oxygen-enriched liquid stream is outlet 1
It is withdrawn from the bottom of the higher pressure rectification column 108 via 38, subcooled in a heat exchanger 140 and flows through a pressure reducing or throttling valve 142. The oxygen-enriched liquid stream produced is 2
It is divided into three tributaries. Such a first tributary is the second
Of condenser-reboiler 128, thereby producing cooling for the condensation of nitrogen vapor withdrawn from high pressure rectification column 108 via outlet 126. The oxygen-enriched liquid inlet first tributary is boiled as a result of heat exchange with the condensing nitrogen vapor, and the oxygen-enriched vapor produced is introduced through inlet 144 at a level below that of inlet 124. It is introduced into the low pressure rectification column 122. Second oxygen-enriched liquid
The tributary is located above the inlet 144, and the inlet 124
The low pressure rectification column 122 through the inlet 146, not below.
Will be introduced to. The further flow of air is through the heat exchanger 104.
Is introduced into the low pressure rectification column 122 by sampling a small portion of the second stream of purified air from between the cold end of the heat exchanger 106 and the warm end of the heat exchanger 106 and passing it through the expansion turbine 148. Is formed for. Turbine 1
The introduction temperature of 48 is typically about 150K. The expanded air produced leaves the turbine 148 at about the pressure of the lower pressure rectification column 122 and passes through the inlet 150 located above the level of the inlet 144 but not below the level of the inlet 124. Enter tower 122. Inlet 12
Low pressure rectification column 1 through 4, 144, 146 and 150
The fluid introduced into 22 is then separated into nitrogen vapor and impure liquid oxygen. The pressure at the top of the low pressure rectification column 122 is typically on the order of 4 bar.

To produce an upward flow of vapor from the bottom to the top of the lower pressure rectification column 122, a liquid flow ("intermediate" flow).
Is withdrawn from the lower pressure rectification column 112 via the outlet 152 at a level such that the liquid contains about 80% by volume oxygen. The intermediate stream flows countercurrently to the second purified air stream through the first condenser-reboiler 114, thus producing cooling for the condensation of the second purified air stream. . The intermediate stream is itself reboiled and the vapor produced is introduced via the inlet 154 into the bottom region of the lower pressure rectification column.

As a result of the separation that occurs inside the low pressure rectification column, an impure liquid oxygen product, which typically contains on the order of 90% by volume oxygen, is formed at the bottom of the low pressure rectification column 122. The impure liquid oxygen product flow is delivered through outlet 15
Is removed from the bottom of the low pressure rectification column 122 via 6.
Impure liquid oxygen product flow is limited to throttle or pressure reducing valve 1
Flows through 58, thereby reducing the pressure to about 1.5 bar. The impure product oxygen stream flows countercurrently to the condensing nitrogen stream through the second condenser-reboiler 128, thereby being vaporized. The oxygen product stream may flow from the second condenser-reboiler 128 sequentially through the heat exchangers 140, 106 and 104, for example, to ambient temperature gasification or metal reforming processes. .

The product nitrogen stream is withdrawn from the top of the lower pressure rectification column 122 via outlet 160 at a pressure of about 4 bar and in turn heat exchangers 132, 140, 106 and 10.
4 through each of them, from its cold end to its warm end. At high pressure, the nitrogen product at about ambient temperature is thereby produced. If desired, the product is heated and then expanded in an expansion turbine (not shown) to recover work from it.

Examples of operation of the plant shown in FIG. 3 are shown in Tables 3 and 4 below.

[0042]

[Table 3]

[Table 4] In the table, liquid and vapor percentages are% deposition and cm ³ / hr are standard cubic meters per hour.

[Brief description of drawings]

FIG. 1 is a schematic process system diagram of a first air separation plant.

FIG. 2 is a schematic process system diagram of a second air separation plant.

FIG. 3 is a schematic process system diagram of a second air separation plant.

[Explanation of symbols]

2,56 Compressor 4,102 Refining device or unit 6 Main heat exchanger 12,108 High pressure rectification column 14,18,24,38,40,46,51,66,1
10, 118, 124 136, 144, 150, 154, 156 Inlet 16 Condenser-reboiler 20, 32, 42, 48, 50, 52, 126, 13
8,152,160 Outlet port 22,128 Second condenser-reboiler 26,34,132,140 Heat exchanger 28,36,44,58,64,116,120,13
4,142,158 Pressure reducing valve or throttle valve 30,122 Low pressure rectification column 60,148 Expansion turbine 100 Main compressor 104,106 Main heat exchanger 112 Booster-compressor 114 First condenser-Reboiler

Claims (12)

[Claims] 1. A first air stream is rectified in a high pressure rectification column,
Thereby producing nitrogen vapor and oxygen-enriched liquid;
Condensing at least some of the nitrogen vapor, using the first stream of condensate produced as a reflux agent in the higher pressure rectification column, and using the second stream of condensate in the lower pressure rectification column. Used as a refluxing agent; withdrawing the oxygen-enriched liquid stream from the high pressure rectification column and rectifying it in the low pressure rectification column, thereby producing an impure liquid oxygen product; A product in liquid form from the low pressure rectification column; a liquid from the low pressure rectification column having an oxygen concentration greater than that of the oxygen-enriched liquid but less than the concentration of the impure liquid oxygen product. Of the low pressure rectification column by removing the intermediate flow of the above, reboiling the intermediate flow by heat exchange with the second air flow, and returning the resulting reboiled intermediate flow to the bottom region of the low pressure rectification column. Liquid reboiled up the street The method of separating air comprising the step of supplying. 2. The method according to claim 1, wherein the intermediate stream has an oxygen content of 50 to 85% by volume. 3. The nitrogen vapor produced in the high pressure rectification column is condensed by heat exchange with the oxygen-enriched liquid,
Thereby, at least a portion of the oxygen-enriched liquid is
The method according to claim 1 or 2, wherein the gas is vaporized in an upstream region of the introduction into the low pressure rectification column. 4. The first and second air streams remove carbon dioxide and water vapor from a compressed air stream, respectively, producing a purified air stream that is the impure liquid oxygen product, and A process according to any one of claims 1 to 3, formed by cooling in a main heat exchanger by countercurrent heat exchange with a nitrogen stream withdrawn from the lower pressure rectification column. 5. The impure liquid oxygen exchanges heat with a third air flow in the main heat exchanger at a pressure higher than either the pressure of the first air flow or the pressure of the second air flow. Is
The method according to claim 4, whereby a third air stream is at least partially condensed and introduced into the higher pressure rectification column, the third air stream being taken from the purified air stream. . 6. A portion of the third air stream is taken therefrom and expanded with the performance of external work in an expansion turbine to the pressure of the high pressure rectification column, and at least one of the expanded air streams. Parts are introduced into the high pressure rectification column,
The method according to claim 5. 7. The method of claim 1, further comprising lowering the pressure of the impure oxygen product and at least partially vaporizing it by countercurrent heat exchange with the condensing nitrogen vapor. The method according to item 1. 8. At least a portion of the second air stream comprises:
The process according to any one of claims 1 to 7, which is introduced into the high pressure rectification column in a downstream region of heat exchange with the intermediate stream. 9. Impurity having a high pressure rectification column for separating a first stream of air into nitrogen vapor and an oxygen enriched liquid, an inlet for the oxygen enriched liquid withdrawn from said high pressure rectification column. A low pressure rectification column for producing a liquid oxygen product, a condenser for condensing nitrogen separated in the high pressure rectification column, the high pressure rectification column and the low pressure rectification using the condensate produced as a refluxing agent. Means for feeding into the column, an outlet from the low pressure rectification column for the impure liquid oxygen product, of the liquid withdrawn from the low pressure rectification column in the region intermediate the inlet and the outlet. A reboiler for boiling the intermediate stream by heat exchange with a second stream of air, and a means for separating the air, including means for returning the reboiled liquid produced to the bottom of said lower pressure rectification column apparatus. 10. The apparatus of claim 9, wherein the condenser is arranged to contain the oxygen-enriched liquid used from the high pressure rectification column. 11. Use of a means for purifying a compressed air stream by removing water vapor and carbon dioxide therefrom, the impure liquid oxygen purified product and the nitrogen stream from the low pressure rectification column. Heat exchanger for cooling said air stream by heat exchange, means for collecting said first and second air streams from said cooled air stream, said refining means and said main heat exchanger 11. A compressor for producing a third air stream from the air stream in a region intermediate between and, and means for passing the third air stream through the main heat exchanger. The described device. 12. An expansion turbine having an inlet communicating therewith with an area of the main heat exchanger through which the third air stream flows and an outlet communicating with the high pressure rectification column. An apparatus according to claim 11.